Development and Identification of Novel Rice Blast Resistant Sources and Their Characterization Using Molecular Markers

To develop and characterize introgression lines for leaf and neck blast resistance, 326 introgression lines were developed using various accessions of six different AA genome wild species in the genetic background of elite Indian varieties like PRl14 and Pusa 44 and were screened for blast resistance. Stringent phenotyping coupled with genotyping using gene based markers led to the identification of four resistant introgression lines, which showed promising resistance and do not possess any of the tested genes. Furthermore, multi-location screening confirmed the field resistance of the four introgression lines to both leaf and neck blast. Molecular characterization of these introgression lines using genome-wide simple sequence repeat markers revealed the presence of small percentage of wild Oryza genome introgrssion. So these lines can be used for mapping and identification of novel leaf and neck blast resistance genes. Thus, these four introgression lines can be considered as new genetic resources for blast resistance.

Antixenosis and Tolerance of Rice Genotypes Against Brown Planthopper

Nine genotypes were evaluated under greenhouse conditions for antixenosis and tolerance against brown planthopper （BPH, Nilaparvata lugens Stal）. In antixenosis studies, proportion of insects settled on a test genotype in relation to the susceptible control TN1 was recorded, with significantly lower proportion of nymphs （55.22%-59.18%）, adult males （60.33%-60.75%）, and adult females （80.56%- 79.26%） settled on RP2068-18-3-5 and Ptb33 in relation to those on TN1. Based on number of feeding sites, the test genotypes were ranked in order from the highest to the lowest as RP2068-18-3-5, Ptb33, MR1523, Rathu Heenati, Sinnasivappu, ARC10550, MO1, INRC3021 and TNI. The order was exactly reverse in terms of fecundity expressed as number of eggs laid per female. In tolerance studies, days to wilt, functional plant loss index and plant dry weight loss to BPH dry weight produced were recorded. RP2068-18-3-5, Rathu Heenati and Ptb33 performed better than the other test genotypes. These results helped in relative quantification of BPH resistance levels in the genotypes. RP2068-18-3-5, a new effective source of BPH resistance, can be used in resistance breeding after tagging of resistant genes/QTLs linked to different parameters of antixenosis and tolerance with selectable molecular markers.

Introgressions from Oryza rufipogon Increase Photosynthetic Efficiency of KMR3 Rice Lines

To understand the wild Oryza genome effect on photosynthesis and its relation to total dry matter accumulation in an elite rice variety, a set of 40 stable introgression lines(ILs) BC_3F_8 derived from a cross of Oryza sativa(KMR3) × Oryza rufipogon(WR120) were grown under well watered conditions. Leaf gas exchange measurements and leaf chlorophyll estimates were conducted at the flowering stage. The results revealed significant variations in net photosynthetic rate(Pn), transpiration rate(E), transpiration efficiency(Pn/E) and carboxylation efficiency(Pn/C_i). Pn showed significant positive correlation with E, stomatal conductance(g_s), Pn/C_i and total canopy dry matter. Specific leaf area and leaf thickness were not significantly correlated with Pn. Thirty-seven out of 40 ILs showed higher Pn than KMR3 [11.28 μmol/(m^2·s)], and 20 ILs showed higher Pn than WR120 [15.08 μmol/(m^2·s)]. The line IL194 showed the highest Pn [21.62 μmol/(m^2·s)] with increased total canopy dry matter followed by lines IL381, IL106, IL363-12, IL198, IL86-18 and IL50, which exhibited Pn above 18.0 μmol/(m^2·s). The ILs with enhanced Pn are a potential source for developing rice varieties and hybrids with higher biomass and yield.

Informative ISSR Markers Help Identify Genetically Distinct Accessions of Oryza rufipogon in Yield Improvement

Inter simple sequence repeat（ISSR） polymorphism was used to determine genetic diversity and phylogenetic relationships in 90 genotypes of wild and cultivated species of Oryza from different geographical regions of the world. In all the 17 primers used in ISSR-PCR, a total of 11 464 bands were amplified at 253 band positions/loci. The primer UBC-809 amplified the maximum bands（1 059） at 21 band positions. UBC-810 and UBC-835 amplified the minimum of 391 bands each at 7 and 14 band positions, respectively. The mean polymorphism information content ranged from 0.44 to 0.84 and resolving power ranged from 8.69 to 23.53. Un-weighted pair group method with arithmetic mean dendrogram and population structure based on the 17 primers separated all genotypes into 4 major clusters with a genetic similarity of 53%–100%. The first two clusters consisted of 30 O. rufipogon accessions each. In the third cluster, O. nivara and O. longistaminata grouped as one sub-cluster and all other O. nivara accessions and cultivars grouped as another sub-cluster. The fourth cluster had only five O. rufipogon accessions which can be a source of new genes. Four sub-populations were identified within O. rufipogon and two sub-populations within O. nivara at K = 7. A subset of six primers with high resolving power values were the most informative and grouped all genotypes almost similarly as the 17 primers did. Use of these six highly informative primers in ISSR-PCR is a cost effective and robust method for assessing genetic diversity in large germplasm collections of wild rice species.

Carbon Nanoparticle Exerts Positive Growth Effects with Increase in Productivity by Down-Regulating Phytochrome B and Enhancing Internal Temperature in Rice

The effects of carbon nanoparticle(CNP)on rice variety Swarna(MTU7029)were investigated.CNP induced effects similar to shade avoidance response(SAR)of Arabidopsis,with increase in shoot length,root length,root number,cotyledon area,chlorophyll content and total sugar content in rice seedlings.In mature plants,CNP treatment resulted increase in plant height,number of productive tillers per plant,normalized difference vegetation index,quantum yield and root growth.A total of 320 mg of CNP per plant administered in four doses resulted in improved grain traits such as filled grain rate,100-grain weight,grain length/width ratio,hulling rate,milling rate and head rice recovery.Seeds from the CNP-treated plants showed increase in amylose,starch and soluble sugar contents compared to controls.Strikingly,CNP treatment showed an average of 17.5%increase in yield per plant.Upon investigation to the molecular mechanism behind CNP induction of SAR,a significant downregulation of phytochrome B transcript was found.Decrease in perception of red wavelengths led to responses similar to SAR.Increase in plant’s internal temperature by 0.5ºC±0.1ºC was recorded after CNP treatment.We suggest that the internalized CNP aggregates may serve to absorb extra photons thereby increasing the internal temperature of plants.Phytochrome B accounts the hike in internal temperature and initiates a feed-back reduction of its own transcription.We suggest that moderate SAR is beneficial for rice plants to improve agronomic traits and yield.It presents a potential non-transgenic method for improving rice yield by CNP treatment.

QTL Analysis for Grain Iron and Zinc Concentrations in Two O. nivara Derived Backcross Populations

Identification of quantitative trait loci （QTLs） for grain mineral elements can assist in faster and more precise development of micronutrient dense rice varieties through marker-assisted breeding. In the present study, QTLs were mapped for Fe and Zn concentrations in two BC2F3 mapping populations derived from the crosses of O. sativa cv Swarna with two different accessions of O. nivara. In all, 10 and 8 QTLs were identified for grain Fe and Zn concentrations in population 1, and 7 and 5 QTLs were identified in population 2, respectively. Eighty percent of the QTLs detected in both populations were derived from O. nivara. Five QTLs for Fe and three QTLs for Zn explained more than 15% phenotypic variance either in interval or composite interval mapping. The locations of O. nivara derived QTLs such as qFe2.1, qFe3.1, qFe8.2 and qZn12.1 were consistently identified in both the populations. Epistatic interaction was observed only between RM106 and RM6 on chromosome 2 and between RM22 and RM7 on chromosome 3 for Fe concentration in population 1. Sixteen candidate genes for metal homeostasis were found to co-locate with 10 QTLs for Fe and Zn concentrations in both the populations. Most of the Fe and Zn QTLs were found to co-locate with QTLs for grain yield and grain quality traits. Some of the major effect QTLs identified can be used to improve rice grain Fe and Zn concentrations.

Yield Traits and Associated Marker Segregation in Elite Introgression Lines Derived from O. sativa × O. nivara

Introgression lines(ILs)derived from interspecific crosses are a source of new genetic variability.A total of 55 ILs derived from two crosses Swarna×O.nivara IRGC81848(population A)and Swarna×O.nivara IRGC81832(population B)were characterized for yield and yield-related traits/QTLs.Segregation of 103 simple sequence repeat(SSR)markers associated with yield-related QTLs was studied.Population A showed an average of 12.6%homozygous O.nivara alleles and population B showed 10.6%.Interestingly,three SSR markers,RM223,RM128 and RM517,showed conspicuous pattern of segregation.The distribution of parental alleles at three loci RM223,RM128 and RM517 linked to yield-related traits was unique.These markers flanked to several yield-related QTLs.RM223,flanking to qyld8.3,was heterozygous in almost all the 55 ILs except in IL10-3S and IL131S.RM128 on chromosome 1 and RM517 on chromosome 3 were mutually exclusive in 46 out of 55 ILs.These 46 ILs showed either of the marker allele RM128 or RM517 from O.nivara but not both.IL166S had both RM128and RM517 from O.nivara and the other ILs showed homozygous Swarna allele at RM517 except IL65S.Population structure assigned the 55 ILs to three sub-populations based on their genomic diversity.IL65S,IL166S,IL248S,IL7K and IL250K showed high yields in multi-location trials,and IL248S was released for cultivation as DRRDhan 40.

Nucleocytoplasmic Trafficking of the Arabidopsis WD40 Repeat Protein XIW1 Regulates ABI5 Stability and Abscisic Acid Responses

WD40 repeat-containing proteins(WD40 proteins)serve as versatile scaffolds for protein-protein interac-tions,modulating a variety of cellular processes such as plant stress and hormone responses.Here we report the identification of a WD40 protein,XIW1(for XPO1-interacting WD40 protein 1),which positively regulates the abscisic acid(ABA)response in Arabidopsis.XIW1 is located in the cytoplasm and nucleus.We found that it interacts with the nuclear transport receptor XPO1 and is exported by XPO1 from the nucleus.Mutation of XIW1 reduces the induction of ABA-responsive genes and the accumulation of ABA Insensitive 5(ABI5),causing mutant plants with ABA-insensitive phenotypes during seed germination and seedling growth,and decreased drought stress resistance.ABA treatment upregulates the expression of XIW1,and both ABA and abiotic stresses promote XIW1 accumulation in the nucleus,where it interacts with ABI5.Loss of XIW1 function results in rapid proteasomal degradation of ABI5.Taken together,these findings suggest that XIW1 is a nucleocytoplasmic shuttling protein and plays a positive role in ABA responses by interacting with and maintaining the stability of ABI5 in the nucleus.